Left Bundle Branch Block

What is left bundle branch block?

Left bundle branch block is a problem with the heart’s electrical wiring system.

Your heart has 4 chambers. The 2 upper chambers are called atria, and the 2 lower chambers are called ventricles. In a healthy heart, the signal to start your heartbeat begins in the upper right chamber of the heart (right atrium). From there, the signal travels to the lower chambers (right and left ventricles) of the heart. As the signal travels, it triggers nearby parts of the heart to contract in a coordinated manner.

In left bundle branch block, there is a problem with the left branch of the electrical conduction system. The electrical signal can’t travel down this path the way it normally would. The signal still gets to the left ventricle, but it is slowed down, as the signal can only use the right branch. Because of this, the left ventricle contracts a little later than it normally would. This can cause an uncoordinated contraction of the heart. As a result, the heart may eject blood less efficiently. For most people, this is not a big problem. However, if you have an underlying heart failure, left bundle branch block can make it worse.

In some people, their left bundle branch block is present all the time. In others, it happens off and on. Exercise, for example, might bring it on for some people.

Left bundle branch block happens more often in older people. It is rare in healthy young people. It usually happens in people who have some type of underlying heart problem.

What causes left bundle branch block?

Left bundle branch block can result from a number of heart conditions. These include:

Coronary artery disease

High blood pressure

Heart valve disease

Cardiomyopathy (enlarged or weakened heart muscle)

Myocarditis (heart infection)

Heart attack

Congenital heart defects

Certain heart rhythm medicines

All of these conditions increase the risk for left bundle branch block. Sometimes, though, left bundle branch block happens on its own even when the heart may be structurally normal. Researchers aren’t sure what causes these cases of left bundle branch block.

What are the symptoms of left bundle branch block?

Usually, left bundle branch block by itself does not cause symptoms. You are more likely to have symptoms if you have other problems in addition to your left bundle branch block. In people with heart failure, left bundle branch block can sometimes make those symptoms worse. In these people, left bundle branch block can worsen shortness of breath and fatigue.

In very rare cases, both the right and left bundles become blocked. This is a form of complete heart block. When this happens, the impulses from the top chambers of the heart do not activate the lower chambers of the heart. This can lead to long episodes in which the heart stops.

How is left bundle branch block diagnosed?

Your doctor can diagnose left bundle branch block with the help of an electrocardiogram (ECG). This test provides information about the heart rhythm. People often first find out they have left bundle branch block when having an ECG done for some other reason.

Your doctor will probably want to check you for other heart conditions associated with left bundle branch block, like high blood pressure and coronary artery disease. This evaluation will include a thorough history and medical exam along with an ECG. It might also include the following tests:

Echocardiogram to examine blood flow in the heart and heart motion

Cardiac stress testing to look for coronary artery disease or other abnormalities

Blood work to assess cholesterol levels and other factors

How is left bundle branch block treated?

In young and healthy people, left bundle branch block is uncommon. If there are no other underlying heart problems, it appears to have little effect on how long you live. You may not need any treatment at all for left bundle branch block. This is especially likely if you have no other disease affecting your heart. People without any symptoms should still undergo careful evaluation.

In older people with coronary artery disease, left bundle branch block is associated with greater risk of death. This is especially true for people with heart failure. Left bundle branch block is also associated with greater risk of death after a heart attack.

Some people may have left bundle branch block for many years without any problems. However, a newly diagnosed left bundle branch block may mean there is some underlying heart condition that requires prompt treatment. An aggressive evaluation may be necessary if you have new onset of a left bundle branch block.

Some people with left bundle branch block may need a permanent pacemaker. This is usually only needed if there are symptoms or another conduction problem along with left bundle branch block. A pacemaker helps ensure that the heart beats at the proper rate.

People with heart failure and left bundle branch block may need cardiac resynchronization therapy or CRT. This is a type of pacemaker therapy that helps the ventricles contract at the same time. CRT can increase the amount of blood that the heart ejects and can improve symptoms of shortness of breath and fatigue.

How do I manage left bundle branch block?

Monitor your symptoms carefully. Make sure you see a doctor regularly, even if you don’t have any symptoms.

Make sure all your doctors know about your left bundle branch block.

Left bundle branch block may make it harder for a doctor to diagnose a heart attack.

When should I call my healthcare provider?

See a doctor right away if you have chest pain, fatigue, transient loss of consciousness, or shortness of breath. If you have any new symptoms, plan to see your doctor soon.

Key points about left bundle branch block

Left bundle branch block affects the heart’s conducting system. The left branch of this conducting system is blocked or partially blocked. This causes the left ventricle to contract a little later than it should. This can cause the heart to eject blood less efficiently.